1. Field of the Invention
The present invention relates to a supercapacitor and a method for manufacturing an electrode thereof, and particularly a method for manufacturing an electrode of a supercapacitor by forming a P-doped carbon substrate and a supercapacitor using the manufactured electrode.
2. Description of Related Art
Energy storage has been a critical concern as the demands of energy supply become challenging in recent years. For instance, high-tech products such as mobile phones and hybrid electric vehicles/electric vehicles require both high energy density and high power supply at the same time. However, even though newly-developed batteries, like lithium batteries and fuel cells, retain very high specific energy, the high power supply still remains to be an issue. Accordingly, supercapacitors, also known as electrochemical capacitors, have attracted plenty of attention because they show the promising potential to meet such energy-storing demands without considering their extremely long cycle life.
According to the charge storage mechanism, supercapacitors are generally divided into three categories: (1) electrical double-layer capacitors (EDLCs) utilizing the electrostatic charge separation at the electrolyte/electrode interface to store electric energy; (2) redox pseudocapacitors employing electrochemically active materials with fast redox reactions at/near electrode surface; and (3) asymmetric supercapacitors consisting of two dissimilar materials with complementary working potential windows to enlarge the cell voltage and promote the energy density of supercapacitors. Supercapacitors have been extensively studied and applied to various fields in recent years, such as energy supply of mobile devices, hybrid/electric vehicles, telecommunications and so on due to their rapid recharge capability, long cycle life, and great peak/pulse power ability in comparison with rechargeable batteries as well as their much higher specific capacitance than dielectric capacitors. Among these, electrodes of the EDLCs and one electrode of the asymmetric supercapacitors are based on the coulombic electrostatic forces of electric charges in the electrical double-layer at the electrode/electrolyte interface. As the specific capacitance is directly proportional to the specific surface area accessible to the electrolyte, it remains an important issue to improve the material and microstructure of the electrode materials.
Carbon materials, such as activated carbon, carbon cloth, carbon nanotubes, graphite, graphene, carbon capsule, etc., can be applied as the electrode materials of EDLCs and one electrode of the asymmetric supercapacitors. Previous studies reported that the performance of supercapacitors can be improved by activating the carbon materials with phosphoric acid. However, the so-called phosphoric acid “activation” is mainly confined to increase the specific surface area of carbon materials, and the improvement is considerably limited. Therefore, it would be advantageous to develop a more efficient electrode material of a supercapacitor and a method for manufacturing the same.